This invention relates to an electrophotographic printing machine, and more particularly concerns an improved stapling apparatus for use therein.
In the process of electrophotographic printing, a photoconductive member is charged to a substantially uniform level, thereby sensitizing the surface thereof. Thereafter, the charged photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive surface discharges the charge selectively in the irradiated area. This records an electrostatic latent image on the photoconductive surface corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoconductive surface, the latent image is developed by bringing a developer mix into contact therewith. The greater attractive force of the latent image causes toner particles to be attracted from the carrier granules of the developer mix to the latent image. Thereafter, the resultant toner powder image is transferred to a copy sheet and permanently affixed thereto. This general approach was originally disclosed by Carlson in U.S. Pat. No. 2,297,691, and has been further amplified and described by many related patents in the art.
Frequently, it is highly desirable to reproduce a set of original documents as a plurality of sets of copies. This may be accomplished by employing a recirculated document handling system in association with the electrophotographic printing machine. The recirculating document handling system is positioned on the platen of the printing machine and advances successive original documents thereto. The original documents disposed on the platen are exposed and subsequently reproduced. After being copied, each original document is returned to the stack of original documents so that it may be re-imaged for the next successive copying cycle. In this manner, collated sets of copies or booklets may be formed. Each set of copies corresponds to the set of original documents. The copy sheets of specific booklets are stapled to one another.
A stapling apparatus is located at the finishing station of the printing machine to staple the set of copies. After the staple has been driven through the set of copies, the legs thereof protrude outwardly therefrom. Thus, it is necessary to bend the legs back into contact with the set of sheets, i.e. to clinch the legs. This may be readily achieved by a clinching mechanism. Various types of techniques may be utilized to achieve clinching. For example, a passive clincher employs an anvil having an appropriately configured groove into which the legs of the staple are pressed. This bends the legs into contact with the sheets. Active systems utilize clincher ears which move from a position spaced from the legs to a position in engagement therewith so as to fold the legs into contact with the bottom most sheet of the set. Hereinbefore, active clinching mechanisms have been driven by pneumatic, hydraulic, mechanical and electromagnetic devices. In clinching mechanisms previously employed, the electromagnetic device must be far larger than is optimum in order to provide the maximum force required over the range of displacement. This is due to the fact that electromagnetic devices, such as solenoids, produce very little force when their cores are extended, thus, they generally develop insufficient force to start the clinching operation when the output force thereof matches the required force to complete the clinching operation.
When a solenoid is selected which develops sufficient force to start clinching operation, the resultant output force produced by the solenoid armature is greater than required to complete clinching of the staple legs. This is due to the fact that at the start of clinching, the core, i.e. armature of the solenoid is fully extended. At completion of clinching the core extension is a minimum. Thus, the force applied by the armature increases as the clinching operation proceeds.
Accordingly, it is the primary object of the present invention to improve the clinching mechanism employed in a stapling apparatus.